Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

The Heart

Name: Anna King

Heart
●

What is the Heart?

The heart is a ​muscular​ ​organ​ in humans and other ​animals​, which pumps ​blood​ through the ​blood
vessels​ of the ​circulatory system​
...


Information on the Heart
In humans, other mammals, and birds, the heart is divided into four chambers: upper left and
right ​atria​; and lower left and right ​ventricles​
...
Fish, in contrast, have two
chambers, an atrium and a ventricle, while reptiles have three chambers
...
The heart is enclosed
in a protective sac, the ​pericardium​, which also contains a small amount of ​fluid​
...

The heart pumps blood with a rhythm determined by a group of pacemaking cells in the ​sinoatrial
node​
...
The heart receives blood
low in oxygen from the ​systemic circulation​, which enters the right atrium from
the ​superior​ and ​inferior​ ​venae cavae​ and passes to the right ventricle
...

Oxygenated blood then returns to the left atrium, passes through the left ventricle and is pumped
out through the ​aorta​ to the systemic circulation−where the oxygen is used
and ​metabolized​ to ​carbon dioxide​
...

​Exercise​ temporarily increases the rate, but lowers ​resting heart rate​ in the long term, and is good
for heart health
...
Of these more than three quarters are a result of ​coronary artery
disease​ and ​stroke​
...
Cardiovascular
diseases frequently have no symptoms or may cause ​chest pain​ or ​shortness of breath​
...
Specialists who focus on diseases of the heart are
called ​cardiologists​, although many specialties of medicine may be involved in treatment
...

The human heart is situated in the ​middle mediastinum​, at the level of ​thoracic vertebrae T5-T8​
...
The back surface of the heart lies near the ​vertebral column​, and the front surface sits
behind to the ​sternum​ and ​rib cartilages​
...
The upper part of the
heart is located at the level of the third costal cartilage
...

The largest part of the heart is usually slightly offset to the left side of the chest (though
occasionally it may be ​offset to the right​) and is felt to be on the left because the ​left heart​ is
stronger and larger, since it pumps to all body parts
...
The heart is cone-shaped, with its base positioned upwards and tapering down to the
apex
...
The heart is typically the size of a fist:
12 cm (5 in) in length, 8 cm (3
...
5 in) in thickness
...

●

The Heart Chambers

The heart has four chambers, two upper ​atria​, the receiving chambers, and two lower ​ventricles​, the
discharging chambers
...
This distinction is visible also on the surface of the heart as
the ​coronary sulcus​
...
The
right atrium and the right ventricle together are sometimes referred to as the ​right heart​
...
The
ventricles are separated from each other by the ​interventricular septum​, visible on the surface of
the heart as the ​anterior longitudinal sulcus​ and the ​posterior interventricular sulcus​
...
It
forms the ​atrioventricular septum​ which separates the atria from the ventricles, and the fibrous
rings which serve as bases for the four ​heart valves​
...
The interatrial septum separates the atria and the interventricular septum separates the
ventricles
...

●

Valves

The heart has four valves, which separate its chambers
...


The valves between the atria and ventricles are called the atrioventricular valves
...
The tricuspid valve has three cusps, which
connect to chordae tendinae and three papillary muscles named the anterior, posterior, and septal
muscles, after their relative positions
...
It is also known as the bicuspid valve due to its having two cusps, an anterior and a
posterior cusp
...

The ​papillary muscles​ extend from the walls of the heart to valves by cartilaginous connections
called ​chordae tendinae​
...
During the relaxation phase of the cardiac cycle, the papillary muscles are also relaxed and
the tension on the chordae tendineae is slight
...
This creates tension on the chordae tendineae, helping to hold the cusps of the
atrioventricular valves in place and preventing them from being blown back into the atria
...
The ​pulmonary valve​ is
located at the base of the ​pulmonary artery​
...
When the ventricle relaxes blood flows back into the ventricle from the artery
and this flow of blood fills the pocket-like valve, pressing against the cusps which close to seal the
valve
...
This too has three cusps which close with the pressure of the blood flowing back from the
aorta
...

The right atrium receives blood almost continuously from the body's two major veins,
the ​superior​ and ​inferior​ ​venae cavae​
...
In the wall of the right atrium is an oval-shaped depression
known as the ​fossa ovalis​, which is a remnant of an opening in the fetal heart known as the ​foramen
ovale​
...

The right atrium is connected to the right ventricle by the ​tricuspid valve​
...
In
addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known
as the ​moderator band​ reinforces the thin walls of the right ventricle and plays a crucial role in
cardiac conduction
...
The right ventricle
tapers into the ​pulmonary trunk​, into which it ejects blood when contracting
...
The
pulmonary valve lies between the right heart and the pulmonary trunk
...
The left atrium receives oxygenated blood back from the lungs via one of the four ​pulmonary
veins​
...
Like the right atrium, the
left atrium is lined by ​pectinate muscles​
...
The left ventricle is much thicker as compared with the right, due to the greater
force needed to pump blood to the entire body
...
The left ventricle pumps blood to the body through
the ​aortic valve​ and into the ​aorta​
...


Heart wall

Layers of the heart wall, including visceral and parietal pericardium
The heart wall is made up of three layers: the inner ​endocardium​, middle ​myocardium​ and
outer ​epicardium​
...

​
The innermost layer of the heart is called the endocardium
...
It is continuous with
the ​endothelium​ of the veins and arteries of the heart, and is joined to the myocardium with a thin
layer of connective tissue
...


The swirling pattern of myocardium helps the heart pump effectively
The middle layer of the heart wall is the myocardium, which is the ​cardiac muscle​ – a layer of
involuntary ​striated muscle tissue​ surrounded by a framework of ​collagen​
...
This complex swirling pattern allows the heart to pump blood more effectively
...
The muscle cells make up the bulk (99%) of cells in
the atria and ventricles
...
The intercalated discs
allow the cells to act as a ​syncytium​ and enable the contractions that pump blood through the heart
and into the ​major arteries​
...
They are generally much smaller than the contractile cells and have
few ​myofibrils​ which gives them limited contractibility
...
Cardiac muscle tissue has ​autorhythmicity​, the unique ability to initiate a ​cardiac action

potential​ at a fixed rate – spreading the impulse rapidly from cell to cell to trigger the contraction of
the entire heart
...
It consists of two membranes: an inner ​serous
membrane​ called the epicardium, and an outer fibrous membrane
...
These help influence the ​heart rate​
...




---